Drying oven



2 She ets-Sheet 1 DRYING OVEN Filed Oct. 27, 19:50

v Feb. 13, 1934. C. c. wmx

Q IVN m-\ r. E

Feb.- 13, 1934. c. c. wlLcox 1,946,923

7 DRYINGOVEN Filed Oct. 21, 1930 'z-sheets-sheet 2 INVENTOR.

Patented Feb. 13, 1934 Carl C. Wilcox, South Bend, Ind., assignor to Thestudebaker Corporation, South Bend, 11111., a corporationof New Jersey Application October 2'],

13 Claims.

fectly as to present'danger of fire.

'Anotherobject of the invention consists'in the utilization of the heating fluid used in a drying operation, as a fire prevention medium. Another object of the invention relates to automatic fire prevention in drying processes.

Another object relates to a novel apparatus,

adapted for use in drying operations, fireprevention means. are put into operation automatically' upon-the failure of proper air circulation in the heating unit for the drying oven.

7 The invention also relates to novel fire prevention means operatedby a drop-in air pressure within the heating unit, when such drop in pressure is sufiicient to create a fire hazard.

A further feature of the invention relates to a drying system in which an electrically operated fan is used as an air circulating means, and in which upon failure of the supply of electric power to the fan,- fire-preventing means are energized. f I

Many otherfeatures'of the invention will be disclosed in the detailed description of the apparatus and process constituting the subject matter of the invention. 7 1

Referring to the, drawings which illustrate. a a

form of apparatus which may be used in the practice of my invention: p v.

I Figure 1 is an elevation partially in section of a'heating'unit for drying ovens and associated elements.

V Figure 2 is a view taken alongsection lines 2-2 of Figure 1. v

Figure 3 is aview taken along section lines Figure 4 is a detail view showing heating ulna, and electric circuits associated-with the heating unit. a a

In high temperature oven operations, and particularly in the drying of lacquered articles, dangerous and destructive fires very frequently occur due to improper functioning of the mechanism associated with the drying ovens. The fires usually occur in the heating unit positioned 1930. Serial so. 491,520 (0134-18) in advance'of the fan dueto the collection of fine particles of the: lacquer on the heating coils; which lacquerhas; a firing point at about the same temperature as the air'which is'blown into the ovens for drying the finish on the automobile bodies." As most'lacquershave apyroxylinbase and use highly volatile and inflammable organic. solvents, constant vigilance must be exercised to insure safe operation of the heating system, 'sinceeven a slight increase in the temperature of the ovens may cause a'fire especi'allywhen there is an interruption or slowing down of the fan causing a decreased flow of air through the heating-unit. e heating units in drying assemblages are usu lly'welllagged, the te'mpe'ra- 1 jture in the heating units rising veryrapidly if circulation ofairthrough the ovens isn'ot maintained at a smooth and constant rate. Thetemperature inlacquer drying ovens is'generally maintained ratherhigh and if thetemperature within the heating unit rises perceptibly above a predetermined point, the lacquer will distill,'-'

collect on the heating elements, and ignite causingafire. in a drying system not having r'nyinvention included therein, there was recently a short interruption in the power which resulted in thestopping of the fan and] within only a few minutes several fires broke out due to a slight accumulation of lacquer dust 'which it very a5 dimcult, if not impossible to remove from the steam pipes in the heating units.

In the application of my invention. I have effectively eliminated the dangers attendantupon the-lacquer-drying processes now known in the art. 1

My invention will be better understood a from the following description of the drawings, in which. I have shown as any. conventional constructionfor drying the finish on automobile 'bodi es or other articles, aheating chamber in' advance of the 'fan'which is operatively connected with the oven to be heated. j The heating unit 1 is provided with an air inlet 2 and an air exit passage 3. Circulation of the air through the heatunit ismaintaimd by a fan 4 preferably of thecentrifugal type. The fan 4 is incased in a. jacket A leading to an oven, not shown, for deliveringthe heated air to the oven for drying the lacquer or-other coating on the' articles to be finished. The fanshaft 5 has a pulley keyed thereon adapted to be rotated by a belt 6 driven from the pulley '7 on the armature shaft 8 of an electrically energizedmotore. The motor and heating unit may be anchored on a suitable on separate foundations, but the use of a comframe 10, or they may be, if desired, mounted mon foundation is preferred.

' The heating unit is heated preferably by means ofsteam supplied through a pipe 11 controlled by a manually w..perated valve 12, the invalve'seats upon which are adapted to be seated oppositely" acting; valves 18 and 17 which are mounted on a common valve stem 18 and held "free-from-axialmovement'thereon,

" During the normal operation the multiple valve is maintained in raised position, the valve l'lbeing held against itsiseat. on the partition plate 15,"and; the valve 16being'in open posi- 'tion. The steam thus passes from the pipe 11 through the pipe 191mm heating coils 20 which the heating unit and courses I outwardly. 'froin the coils 20 through a steam trap 21 and outlet pipe22.

.r Thejvalvestem 18 is operated by aimean s of a solenoid-23 which is energized by currentsupplied leads 24 and25which connect with" thepowersource whichsupplies currentthrough the motor [9. .Under normal operating conditions, the solenoid 23" is supplied with current rand thev valve stem to its upper, position, maintaininggthe valve 16 open and the valve 17 closedQas shown inFigure 1. If the solenoid 23 function at any time during the dryoperation, the valvestem 18 drops closing, the wee s and opening the valve 17, thus shutting :o'fl the admission of fresh steam into thelheating coils 20. Thus when theva'lve 16 is closed and the valve 1': is. opened," thest'eam inthe heat ing coils 20 expands against -.reduced pressure flows in a reverse direction through {the opening in thedivision plate '15 through'the pipe is sprayed into the interior of the heating unit through the spray nozzle 35.

Itwill thus beseen that if, for any reason ,the circulating means ceases to function' properly that the supply of steam to the-heating unit is cutoff and that immediately steam is sprayed over the heatingcoils 20 which will prevent or ut out anyflre caused by theignition of the lacquer dust whichjha's been permitted to on the heating coils withinfthe heat-f l As a further provisionlfor regulating the, op-

accumulate eration of the valves 116 and, 17, there is con-p *nectedin series' with the primary coil of, the

, unitan'air flow switch 26 which maybe of conventional design and which isfadapted to main- I tain the solenoid circuit closed when the dynamic pressure caused by proper air circulation through heating unit is above a predetermined min imum. 'If' the fan;4"ceases to function, orjif,

f for. anyreason, the circulation of the air ceases orthe pressure caused by the air circulation drops'below such minimum, the switch automatic'allv breaks the solenoid circuit ahdjthe valve stem falls'toits lower positiomclosing the yalve 16 againstjth inflow of steam and] opening I the valve 17'!v so that there will be a reversedfflow ofsteam which will pass thro'ughthe opening in the division plate 15 into the pipe 34and spray throughthe spray nozzle 35 on to theheat "ingcoil 20, v I

One rem of air switch which may be'isatis factoriLv used is shownflin Figure 3. The casing 27 for enclosing theswitch mechanism is mounted in the air exit passage 3 or on the tan casing ature in the oven sufliciently elevated to dry the A by means of a tubular member 28 which is opened at its inner end to the air pressure within the exit passage or fan casing. The outer-end oi the tube 28 is adapted to be closed by means of a flat valve 29 fastened to a valve arm 29' which is loosely mounted for; limited pivotal movement'on pins 30 and 31. A mercury switch 32 is fixed to the valve arm 29' by means of a bracket 33 and is provided with leads '36 and 3'7 which form a series of connections'with leads 24 and 25 and with the power source for the motor 9. The valve arm 29' is preferably so mounted on the pins 30 and 31 that'the valve 29 is out of contact with the end of the tube 28 when the fan 4 is inoperative or when the air circulation is belowa given minimum. When the valve 29 is in closed position the switch contacts will be bridged by the body of mercury within the switch envelope 32 and when the valve 29 is opened, the bridge willjbebroken. e

It will thus be seer that-When the air circulating medium is functioning properly that the ,valve 29 will seat. against the end of the tube 28 andthemerc'ury'switch will function to energize thesolenoid23 so that the valve stem 18-will1be raised,opening the valve 16 and closing thevalve 17 so that the inflow of steam into the heating unit is unrestricted. Upon the air circulating medidmceasihg to function properly; the bridge 'between'the' lead wires 36 and 37 is broken, open ing the electric circuit leading to the solenoid 23 which will permit the valve'ste'm 18 to drop, closing the 'valve 16 andbpening, the valve '17 to thus prevent the inflow. of steam into the heating, unit and topermit the reverse new of steam, all asfabove described whereby the steam escapes through the spray nozzlej35 on to, the heater coils 20; t

A manually operated switch 38 may be placed in the line leading from the power source, and 116 f if desired,; the manually operated. switch 39 may 1 in Figure 4." a V, a v

Theoperation of thedevice is as follows:

take thepplace of the air switch, as illustrated V The article tobe dried is, placed in the oven, 12 I tained in order to constantly sweep these ma- 3 terial's from the heating unit, and likewise v to induce sufficient air into the oven toinsure pro The air switch closes, the solenoid circuit, raising the'valve stem '18 and steam is admitted to the heatingcoils 20 by superatmosphericprese sure, preferably around '100' lbs. per square inch and at a temperature suflicient 'to'heat the'coils 20 at about'300 F. This will create a temper- 4O 1 lacquer; and at aboutthe ignition temperature of the lacquer dust which, as above explained.

will Jignite very quicklywhen the circulation of the air in the heating unit is reduced by the slowing down or stopping of the fan. In'the event the power to the motor fails and the rotation of the fan is retarded or'zstops and the circulation of the air is reduced, the heater coils will quickly heat up and the lacquer dust which has s ttled on the heating coils will distill. and

'will readily ignite to cause a damaging fire as long as combustion supporting atmosphere obtains in the heating unit.

However, in the apparatus above described, if the power fails the solenoid is no longer supplied with current and the valve 16 is closed, cutting off the supply of steam and the valve 17 is opened. The flow of steam in the coils 20 will be reversed'since the pressure imposed on it drops to the pressure in the heating unit, which is approximately atmospheric, and which will be sprayed through thenozzle 25 on to the heating coils 20.

The steam in the coils, together with the aqueous condensate which will flash into steam upon the reduction of the pressure, has been sufficient to create an admission which will not support combustion. I

Although the most common case of failure of the air circulation is due to power failure, it sometimes happens that a breakage occurs in the fan, or forsome other reason, the fan functions improperly. Whenever the air circulation drops toa predetermined danger point, the air pressure diminishes proportionately; and the valve 29 of the air switch rocks the mercury envelope 32, breaking the solenoid circuit and closing the steam inlet valve 1 6. The reverse flow of the steam into the heating unit then takes place in the manner previously described.

It will be understood from the above descrip-' tion of the preferred form of the invention that fire hazards in heating units for drying ovens for lacquered articles may be substantially eliminated by the practice of my invention. The details ofmy novel apparatus and'process are susceptible of a considerable range of variation without departing from the concept of the invention and, therefore,'it is not my intention to be limited to the exact details of construction shown, but on the contrary I desire to claim my invention broadly as well as specifically as indicated in the appended claims, the above detailed description being merely illustrative of the invention and not limiting the same.

Having thus described my invention, what I claim is:

1. A prooes for eliminating fire hazards in the drying of highly combustible materials comprising heating a heating chamber for a drying oven by indirect heat exchange with a heating fluid, circulating air through the heating chamber, and introducing into theheating chamber upon failure of proper air circulation, the fluid from said heat exchange which will create in the heating chamber an atmospherewhich will not support combustion.

2. A process for eliminating fire hazards in the drying of highly combustible materials compris ing heating a heating chamber for a drying oven by indirect heat exchange with a heating fluid, circulating air through the heating chamber, and automatically introducing into the heating chamber upon failure of proper air circulation, the fluid from said heat exchange which will create in the heating chamber an atmosphere which will not support combustion.

3. A process for eliminating fire hazards in the drying of highly combustible materials comprising heating a heating chamber for a drying oven by indirect heat exchange with a non-combustible heating fluid, circulating air through the heating chamber, and upon failure of proper air circulation shutting off the supply of fluid to said heat exchange and discharging a portion of the heating fluid in said heat exchange sufllcient to create in the heating chamber an atmosphere which will not support combustion.

4. *A process for eliminating fire hazards in the drying of combustible materials comprising heatply of heating fluid to the heating chamber upon a failure of proper air'circulation through the heating chamber, and thereafterintr'oducing into the heatingchamber a portion of said heating fluid sufficient to create Within the heating chamberan atmosphere which will not support 'combustioni 5. A process for eliminating fire hazards in the 'dryingof combustible materials which comprises heating a heating chamber for a drying even by indirect-heat exchange with anon-combustible heating fluid, circulating air through the heating *chambenautomatically cutting/01f the supply of heating fluid upon a failure of "proper aircirculated, and then introducing directly. into the heating chamber heating fluid previously passed in indirect heat exchange with the heating chamber, in an amount suflicient tocreate withwill not support combustion.

-in the heating chamber an atmosphere which 6. A process for eliminating fire the drying of combustible material comprising hazards in* heating a heating chamber for a drying oven by indirect heat exchange with a non-combustible heating fluid, circulating air through the heating chamber, and introducing a portion of said heating fluid into the heating chamber upon a failure of proper air circulation, in an amount sufllcient to create in the heating chamber anatmosphere which will not support combustion, said introduction of heating fluid being controlled by the pressure of air induced by the circulation of air through the heating chamber. 7. A process for eliminating fire hazards in the drying of combustible materials comprising heating a heating chamber for a drying oven by indirect heat exchange with a non-combustible heating fluid, circulating air through the heating chamber by power means, and introducing into the heating' chamber, upon failure in the supply of 'said power, a portion of said heating fluid in an amount suflicient to create an atmosphere which will not support combustion.

' 8. A process for eliminating fire hazards in chamber, an air inlet passage therefor, an air 7 outlet passage therefor, means for effecting a 7 circulation of air through the heating chamber, means for supplying a non-combustible heating fluid in indirect heat exchange with the heating chamber, means put into operation by a failure in air circulation for cutting off the supply of heating fluid to the heating chamber,and means for introducing a portion of the heating fluid chamber, an air inlet passage therefor, air

outlet passage therefor, means operated by, elec-r trical; power 'i'or eflecting a circulation chair I through the heating chamber, means ior supply' ing noncombustible'heating fluid in indirect; heat exchange with the heating chamber, means for cutting ofl the supply, of heating fluid upon ajfailureof electrical power, to said last-named means and means put intooperation when, the

f sun l ci heating iluidis cut on ionintroducvl5,

ing chamber inan amount sufllcientto create an .ing aiportionot the heating fluid into heat,-

atmosphere which will-@notsupport combustion;

chamber, an airinlet passage, an airoutlet; pas- J ;sage. and means for electing ;a circulation of air through the heating achamber, steam coils for heating the heating chamber; a steam gpipe i'or supplyingsteam-to-,-the coils, a valve ior controllinsthe flow oi steam 'in saidpipepand means iorjoperating the valve, responsiveto the cii'culatlonv of air'in-the heating chamber.

12. An apparatus suitabletor use in-drying I y'combustible materials comprising a heating;

nceepas chamber, an air inlet passage, an air outlet passage, and 'rneansfor efiecting a circulation of air through the heating chamber, steam coils for heating the heating chamber, a steam pipe for supplyingsteamjo the coils, a valve forcontrolling the flow of, ;S$8- inrr said pipe, means responsive to a iailure in. air circulation for operatingthe valve to cut off the steam'supply,

and means associated with said last named means for introducing steam trom theheating coils into thegheating chamber when the steam supply iscutofl' H 13. {in apparatus suitable for use in. drying combustible materials comprising va heating chamber, anair inlet passage, an air outlet pas- ,sage,- meansifor effecting a circulation of air 1 throughthe heating chamber, operated by elec- 11. An apparatus 1 suitable for I drying 1 combustible materials comprising a heating trical power, steam coils for heating the heating L chamber, .a' steam pipe for supplying steam to thesteam coils, avalve for controlling the sup- 'ply of steam to the coils, meansresponsiveto a failurein the; electrical power supplied .to the airQcirculating means for operating the valve to .cut off thesupply of steam, and means associated with said last, named means'tor introducing steam from the heating coils toithe heating chamber, when the steam supply is cutofl.

' 'CARLC. wnicox. 

